TWI568888B - Gas-diffusion electrode - Google Patents

Description

Gas diffusion electrode and its preparation method and electrochemical cell

The invention relates to a gas diffusion electrode structure, which is suitable as a gas-consuming anode or cathode in an electrolytic cell.

The use of gas diffusion electrodes has been found in several electrochemical processes, especially depolarization processes, whether used as hydrogen-consuming anodes or oxygen-consuming cathodes, and in fuel cell applications. The gas diffusion electrode is usually composed of a porous gas diffusion thin layer, and the device is hydrophobic, and the gas is transported over the thickness thereof, and a catalyst is additionally provided, embedded or laminated on the current collecting member. The current collecting member can also be used as a reinforcing member depending on the final use. Examples of current collecting members are drawing or braiding metal, metal foam, braided or standard carbon cloth or metal cloth or felt, carbon paper. The gas diffusion layer may be made of a conductive powder catalyzed by a catalyst, such as a metal, an oxide or a carbon powder, and a binder, usually a plastic material capable of forming a suitable network to obtain a conductive powder. Composition of a solid composition. The gas diffusion layer is not a self-supporting member, and is usually formed on the current collecting member by various techniques such as spraying an aqueous suspension of the component or by gravure coating or knife coating of an aqueous slurry or paste. The gas diffusion layer can also form a pattern on an inert carrier, and after being laminated with the current collecting member, it is removed by stripping or leaching; and a gas diffusion layer is formed, followed by lamination, which is a very complicated operation, and the gas diffusion layer is usually thin and brittle. It is difficult to dispose of. The gas diffusion electrode may have a catalyst, be added to the gas diffusion layer, or be catalyzed by applying a suitable catalyst layer on the top side of the gas diffusion layer, usually on the opposite side of the current collecting member. Such a configuration results in dimensional dimensioning and poor rigidity of the thin electrode members, which must be adequately supported by suitable spacers and current collectors, as is well known in the art.

The gas diffusion electrode can be used for depolarization acylation; for example, chloralkali electrolysis can be carried out by oxygen to the gas diffusion cathode instead of releasing gaseous hydrogen at the metal cathode, and the associated energy is saved by about 30%. However, in an oxygen-consuming cathode in a chlor-alkali battery, it is necessary to face the gas chamber on one side and the liquid electrolyte chamber on the other side, where a caustic solution is formed. Gas diffusion electrodes are known to be unacceptable for industrial electrolytic cells (ie, the total height exceeds 30 cm) The liquid drop of the caustic solution product can only be remedied to a certain extent by the gas chamber pressurization. The pressure applied by the liquid column is actually higher at the bottom than at the top, unless special countermeasures are made to complicate the design of the battery, such as the cumbersome airbag design of WO 03035939, which is not only costly, but also less reliable, or as WO A filter type battery disclosed in 03042430. The filter member can effectively break the liquid drop in the liquid chamber, and on the other hand, it is expensive and increases the unnecessary resistance drop to the battery construction. The extractor is actually composed of a porous body of a minimum thickness filled with a liquid electrolyte, and can be used as a spacer between the gas diffusion electrode and the separator separator when needed to remedy the gas diffusion electrode dimension definition and poor rigidity, the latter This makes it unsuitable for defining a clear gap chamber of sufficiently low thickness.

In addition, in electro-metallurgical applications, such as metal electro-metallurgy, it is possible to benefit from the energy-saving associated with depolarization in the anode side, in which case the metal electrode deposition is actually carried out on the cathode side of a suitable electrolytic cell at the anode. Release oxygen. The replacement of oxygen by the oxidation of hydrogen by a suitable gas diffusion electrode results in high energy savings, but it is difficult to achieve the mechanical characteristics of the gas diffusion electrode, so that it is not suitable for compartmentalizing a narrow gap chamber, thus limiting its use in The electroforming process typically does not distinguish electrolytic cells. Further, in this case, it is known that the gas diffusion electrode cannot withstand the liquid drop of the electrolytic solution commonly used in industrial electrolytic cells.

Therefore, there is an urgent need to provide a gas diffusion electrode with improved mechanical properties, which is suitable for operation as a self-supporting member, has a small construction tolerance, and is sufficiently rigid to distinguish a narrow gap chamber of the electrolytic cell, and can provide a hydrostatic barrier, which is suitable for bearing an industrial electrolytic cell. Typical liquid drop, for example 20 kPa or more.

The gist of the invention is within the scope of the appended claims.

A gist of the present invention relates to a gas diffusion electrode having a high modulus of elasticity, comprising a gas diffusion layer on a laminated reinforcing member, especially a gas composed of a sintered and cast conductive powder/fluorinated binder composition. The diffusion layer, the longitudinal gas (in-plane) elastic modulus of the build-up gas diffusion layer/reinforcing member assembly is at least 10,000 MPa; in one embodiment, the gas diffusion layer/reinforcing member The longitudinal elastic modulus of the assembly is in the range of 15,000 to 120,000 MPa. In one embodiment, the vertical (out of plane) modulus of elasticity of the gas diffusion layer exceeds 500 MPa. The present inventors have found that a pre-sintered composition of a fluorine-containing binder is cast under the condition that a rubber-like gas diffusion layer can be obtained, so that the gas diffusion electrode imparts a high elastic modulus to the obtained electrode, so that it can withstand extremely high The liquid drop (for example, a liquid drop of more than 20 kPa, such as 80 kPa), and distinguish between the clear gap chambers in the cell, without spacer elements in between. In one embodiment, the reinforcing member of the gas diffusion electrode, selected from the group consisting of tensile or braided metal, metal foam, carbon or metal cloth or felt, can withstand the sintering and casting steps of the process. This advantage is to further enhance the rigidity and dimensional definition of the resulting gas diffusion electrode. In the next preferred embodiment, carbon paper may also be used, if the manufacturing conditions are appropriately selected. In one embodiment, the sintered and cast composition of the gas diffusion layer contains carbon black as a conductive powder, such as a low surface carbon black such as Shawinigan Acetylene Black (SAB). This advantage is to have a suitably strong and electrically conductive layer. In one embodiment, the fluorinated binder in the composition is sintered and cast, and is a perfluoro binder such as PTFE, FEP or PFA. This advantage is to provide a gas diffusion electrode that promotes stability in an electrolyte environment, and facilitates the achievement of a rubbery gas diffusion layer under moderate pressure and temperature conditions. In a specific example, by setting the weight ratio of the sintered and cast component carbon powder to the fluorinated binder between 1 and 2, appropriate mechanical and electrical properties can be obtained. In a specific example, the gas diffusion electrode can be catalyzed by depositing a catalyst layer on the opposite side of the reinforcing member as described above on the gas diffusion layer. There are several types of catalyst layers that can be bonded to the sintered and cast gas diffusion layer: in a specific example, starting from the dispersion of the liquid ionomer suspension or the catalyst powder in the solution, the catalyst layer can be obtained as a recast Ionomer layer. This has the advantage of imparting ionic conductivity and hydrophilic properties to the gas diffusion electrode and can be used for several purposes. In another embodiment, the catalyst layer is also comprised of a sintered and cast composition, such as a sintered and cast carbon-loaded catalyst powder/fluorinated binder composition, laminated to a gas diffusion layer. This has the advantage of further enhancing the dimensional definition and rigidity of the gas diffusion electrode.

Another gist of the present invention relates to a method for preparing the gas diffusion electrode described above. The steps are as follows: adding a fluorinated binder and a conductive powder to the paste, for example, starting from an aqueous suspension or emulsion of a fluorinated binder, and allowing the binder to sink with a suitable chemical agent, such as a light alcohol. Analysis, mixing the precipitated binder with a conductive powder such as carbon black; calendering the paste into a thin layer, for example, having a thickness of less than 2 mm, in a specific example, less than 0.2 mm; The machine is laminated on the reinforcing member at 100-150 ° C and a pressure of 12-24 kPa until a laminated structure is obtained. In one specific example, it takes 15-60 minutes; heating to 300-400 ° C, and regulating to 25- 50 kPa, until the aqueous phase is removed, in a specific example, each takes 15-60 minutes; pressure is released to atmospheric pressure, causing complete sintering under relaxed conditions, which has the advantage that the gas diffusion layer is tightly bonded to the reinforcing member, In a specific example, it takes 1-15 minutes; the sintered structure is cast at 300-400 ° C and a pressure of 30-60 kPa in a heating press until a rubber-like gas diffusion layer is cast, and a high longitudinal elastic modulus is imparted to the assembly. The number, in a specific example, takes 15-60 minutes.

Still another object of the present invention is to an electrochemical cell comprising a gas chamber and a liquid chamber separated by a gas diffusion electrode as described above; the gas diffusion electrode can function as a gas diffusion anode, oxidizing a hydrogen-containing flow on a surface thereof, or as a gas diffusion cathode , on the surface of the oxygen-containing flow, such as pure oxygen or air reduction. In a specific example, the liquid chamber having the gas diffusion electrode separated from the gas chamber establishes a liquid drop of 20 kPa or more, which has the advantage of increasing the gas diffusion layer capacity to withstand the pressure of the liquid column without flooding. The electrolytic cell of the present invention can be a hydrogen depolarization electrolytic metallurgy battery, an oxygen depolarized chlor-alkali battery, an electrodialysis battery for splitting and depolarizing on either side or both sides (ie, a gas diffusion anode provided with hydrogen feeding gas and/or Or gas diffusion cathodes that feed oxygen, as described above, but other types of electrolytic cells or fuel cells, such as alkaline fuel cells, also have the advantages of the gas diffusion electrodes described above, as is well known to the skilled artisan.

The following examples are included to demonstrate particular embodiments of the invention, and their applicability has been largely demonstrated within the scope of the claims. The technologists are aware that the compositions and techniques disclosed in the following embodiments represent the compositions and techniques that the inventors have found to be sufficiently functional in the practice of the present invention; however, the skilled artisan knows that in light of the present disclosure, Many changes can be made in a particular embodiment, and the same or similar results can still be obtained without departing from the scope of the invention.

Example 1

Take a commercial PTFE aqueous suspension from DuPont, USA, and precipitate into a 50:50 volume mixture of 2-propanol and deionized water. The precipitated PTFE was mechanically mixed with Shawinigan Acetylene Black (SBA) commercialized by Cabot Corp., USA, with a carbon to PTFE weight ratio of 60:40. The dough consistency material was immediately passed through an extruder and processed into a 10 cm x 10 cm x 0.1 mm layer using a roll. The layers were laminated on different samples of the silver mesh using a heating press. The mesh has a hole width of 0.50 mm, a wire diameter of 0.14 mm, and a specific gravity of 0.53 kg/m ² . The process is carried out in multiple steps, first at 17.9 kPa and 120. Pressurize at °C for 30 minutes, then adjust the temperature to 335 °C, pressurize to 44.8 kPa, and then release the pressure for 30 minutes, expose the laminated structure to the surrounding air for 5 minutes, and finally the assembly at 34.5 kPa and 335 °C. Pressurized for another 30 minutes.

All samples obtained were measured by dynamic mechanical analysis (DMA) for longitudinal (in-plane) elastic modulus in the range of 35,000 to 49,000 MPa.

Example 2

The procedure of Example 1 was repeated, using 280 μm thick TGP-H-090 carbon paper commercialized by Toray, Japan as a reinforcing member. According to the calendering of Example 1, the SAB/PTFE layer was obtained and laminated on each carbon paper sample; the process was carried out in multiple steps, and the assembly was first pressurized at 13.7 kPa and 120 ° C for 30 minutes, and then adjusted to 335 ° C, and the pressure was increased. After 27.5 kPa, and then depressurized for 30 minutes, the laminate structure was exposed to ambient air for 5 minutes, and finally the assembly was repressurized at 34.5 kPa and 335 ° C for another 30 minutes.

All samples obtained were measured longitudinally using dynamic mechanical analysis (DMA) In-plane) elastic modulus, in the range of 16,000 to 23,000 MPa.

Example 3

The procedure of Example 1 and 2 was repeated using commercial US Textron Systems Corporation of 0.75 mm thick carbon cloth AvCarb ^TM 1243, as a reinforcing member. The SAB/PTFE layer was calendered according to the foregoing embodiment, and laminated on each carbon cloth sample; the process was carried out in multiple steps, and the assembly was first pressurized at 20 kPa and 120 ° C for 30 minutes, and then tempered to 335 ° C. The pressure was raised to 45.5 kPa, and after 30 minutes, the pressure was released, and the laminated structure was exposed to the surrounding air. After 5 minutes, the assembly was finally pressurized at 55 kPa and 335 ° C for another 30 minutes.

All samples obtained were measured for longitudinal (in-plane) elastic modulus using dynamic mechanical analysis (DMA), in the range of 45,000 to 73,000 MPa.

Example 4

Taking a gas diffusion electrode obtained in Example 1, a silver mesh reinforced member, and a gas diffusion electrode obtained in Example 3, on the carbon cloth reinforced member, an opening having a diameter of 8 cm in an experimental apparatus made of a beaker. Used as a pressurized area and tested for air permeability under pressure.

Place the metal ring and the fine mesh into the beaker as the support for the electrode sample. The loop/mesh insert should be flush with the edge of the beaker to prevent any major deflection of the electrode sample. Place it on the edge of the beaker for testing and place a 2 mm rubber gasket. Take the second beaker on the top of the assembly and also place the rubber gasket. Place the top beaker approximately 5 cc of water before sealing. Use a vacuum pump to remove air from the bottom beaker while monitoring the pressure, pause at approximately 7 kPa, maintain pressure, and check for leaks until the maximum pressure is approximately 80 kPa, which is the maximum reachable for the experimental setup.

The sample of Example 1 (intensified with a silver mesh) was able to withstand a pressure of 20 kPa, while the sample of Example 3 (fortified with carbon cloth) was pressed until about 80 kPa, and no leakage was observed.

Example 5

An experimental electrolytic metallurgy battery equipped with a conventional lead-silver (Pb0.75Ag) anode plate and an aluminum cathode, having an active area of 50 cm ² and a gap of 1 cm, for testing from high-purity ZnO and reagent-grade sulfuric acid dissolved in deionized water The obtained barium sulfate electrolyte containing 50 g/l Zn and 170 g/l H ₂ SO ₄ is deposited with zinc as follows: 2 ZnSO ₄ +2 H ₂ O → 2 H ₂ SO ₄ +2 Zn+O ₂ Tested at 500 A/m ² and a total battery voltage of 3.1 V.

Taking an electrode sample of Example 3, on the opposite side of the carbon cloth member, using a printing ink containing a Pt catalyst carried by Vulcan XC-72 carbon black dispersed in an Aldrich commercial liquid Nation suspension, gas diffusion electrode. The coated electrode sample was dried at 125 ° C and a catalyst-containing ionomer film was recast on the surface.

The lead-silver anode of the electrolytic metallurgy battery was used to change the catalytic gas diffusion electrode thus obtained, and was installed in an appropriate frame with the catalytic surface facing the cathode with a gap of 1 cm. The gas diffusion electrode is supplied with pure hydrogen from the back side to continue the electrowinning process of zinc. Found at a current density of 500 A/m ² , the battery voltage drops by 850 mV. The battery is operated overnight without a short circuit.

Example 6

A gas diffusion electrode was prepared as in Example 1, except that the gas diffusion layer was laminated on the opposite side of the silver mesh member to form a 1 mm thick catalyst layer. The process was to precipitate the same aqueous PTFE suspension into 2-propanol and deionized water. In a 50:50 volume mixture, the precipitated PTFE and the silver powder are mechanically mixed, and 5% by weight of platinum powder is mechanically mixed so that the weight ratio of Ag-Pt to PTFE is 80:20, and the obtained paste is Roll extrusion. The lamination, firing and casting steps were carried out in accordance with Example 1, i.e., a gas diffusion electrode was obtained, and the longitudinal (in-plane) elastic modulus was 41,000 MPa.

The obtained electrode was assembled into a gas diffusion cathode (10), a non-porous flat element (9), and a gap between the cathode (10) and the separator (16) in an experimental chloralkali battery according to Example 1 and Figure 1 of WO 03042430. It is 1 mm. The battery can be used at 400 amps (4000 A/m ² ) and the battery voltage is 2.4 V (the optimal battery pressure is about 200 mV lower than that of the low-modulus gas diffusion cathode of the prior art, and the plastic between the cathode and the diaphragm is plastically filtered. Element), work overnight, to make 32% by weight of caustic soda.

The foregoing is not intended to limit the invention, and may be used in accordance with various specific examples without departing from the scope of the invention.

The word "including" is used in the scope of the present specification and the patent application, and does not exclude the existence of other elements or additives.

This specification refers to documents, regulations, materials, devices, articles, etc., the purpose of which is purely to provide the context of the present invention, and does not claim or represent any or all of these matters to form part of the prior art basis, or the relevant field of the present invention. General knowledge of the scope of patent applications in this case prior to priority.

Claims (14)

A gas diffusion electrode comprising a gas diffusion layer laminated on a reinforcing member, the gas diffusion layer being composed of a sintered and cast conductive powder/fluorinated binder composition, and a longitudinal direction of the gas diffusion layer/reinforcing member assembly The modulus of elasticity is at least 10,000 MPa. The gas diffusion electrode of claim 1, wherein the gas diffusion layer/reinforcing member assembly has a longitudinal elastic modulus in the range of 15,000 to 120,000 MPa. A gas diffusion electrode according to claim 1 or 2, wherein the reinforcing member is selected from the group consisting of a tensile metal, a braided metal, a metal foam, a carbon or a metal cloth or a felt material. A gas diffusion electrode according to claim 1, wherein the conductive powder system in the composition is carbon black. A gas diffusion electrode according to claim 1, wherein the fluorinated binder in the composition is PTFE, PFA or FEP. A gas diffusion electrode according to claim 4 or 5, wherein the weight ratio of carbon black to fluorinated binder in the composition is in the range of 1 to 2. The gas diffusion electrode of claim 1 further includes a catalyst layer deposited on the gas diffusion layer on the opposite side of the reinforcing member. The gas diffusion electrode of claim 7, wherein the catalyst layer is composed of a recast ionomer layer containing a catalyst powder. A gas diffusion electrode according to claim 7, wherein the catalyst layer is composed of a sintered and cast carbon-supporting catalyst powder/fluorinated binder composition laminated on the gas diffusion layer. A method for producing a gas diffusion electrode according to any one of claims 1 to 9, comprising the steps of: a. obtaining a paste comprising a fluorinated binder and a conductive powder; b. calendering the paste into Layers having a thickness of 2 mm or less; c. laminating the layers under a heating press at a temperature of 100 to 150 ° C and a pressure of 12 to 24 kPa, and laminating the reinforcing member to obtain a laminated structure; d. Adjust the temperature to 300-400 ° C, and increase the pressure to 25-50kPa; e. release pressure to atmospheric pressure, expose the laminate structure to the air, causing sintering; f. put the sintered structure under the heating press at a temperature of 300 -400 ° C and pressure 30-60 kPa casters. The method of claim 10, wherein the step c, d, f is 15 to 60 minutes, and the exposure to atmospheric pressure air in step e is 1 to 15 minutes. An electrochemical cell comprising at least one gas chamber and a liquid chamber separated by a gas diffusion electrode according to any one of claims 1 to 9, wherein the gas chamber is an anode chamber for oxidizing hydrogen flow on the surface of the gas diffusion electrode, Or a cathode chamber that reduces oxygen flow on the surface of the gas diffusion electrode. An electrochemical cell according to claim 12, wherein a liquid drop of at least 20 kPa is established in the liquid chamber. An electrolytic cell according to claim 12 or 13 is selected from the group consisting of a hydrogen depolarized electrolytic metallurgy battery, an oxygen depolarized chloralkali battery, a depolarized electrodialysis battery, and a fuel cell.